Is there a way to say “method returns this” in Java?

Question

Is there a way to say \"this method returns this\" using Generics?

Of course, I want to override this method in subclasses, so the declaration should wo

Answer 1

You can do something very clever (and akin to what they have done in Scala with the 2.8 collection framework). Declare some interface method that should return "itself" (Note: This is a type parameter, not a keyword!)

public interface Addable> {
   public This add(T t);
}

Now declare a level of indirection - a "template" class

public interface ListTemplate> 
    extends Addable{
}

public interface List extends ListTemplate> {
}

Then an implementation of List has to return a List from the add method (I'll let you fill in the impl details)

public class ListImpl implements List {

    public List add(A a) {
        return ...
    }
}

Similarly you could have declard a SetTemplate and a Set to extend the Addable interface - the add method of which would have returned a Set. Cool, huh?